Sewn fabric filter medium and method of manufacture



C. A. LEE

A ril 14, 1970 SEWN FABRIC FILTER MEDIUM AND METHOD OF MANUFACTURE Original Filed Feb. 8, 1965 flZVEH tar C/rar/ssA. Lee

US. Cl. 210--491 United States Patent 3,506,133 SEWN FABRIC FILTER MEDIUM AND METHOD OF MANUFACTURE Charles A. Lee, Knoxville, Tenn., assignor, by mesne assignments, to Appleton Wire Works Corporation, Appleton, Wis., a corporation of Wisconsin Original application Feb. 8, 1965, Ser. No. 431,030. Divided and this application May 6, 1968, Ser. No. 739,598

Int. Cl. B01d 39/08 6 Claims ABSTRACT OF THE DISCLOSURE A non-woven filter fabric is formed by sewing a layer of substantially straight and parallel laterally independent rack filaments together by sewn filaments stitched in closely spaced discrete parallel rows transversely across the rack filaments. A non-woven filler is sewn to the rack filaments preferably using different sewn filaments on each side of the filler to provide different qualities for the two sides of the resulting fabric. The rack filaments, sewn filaments and filler are then bonded together, as with a resin. The filler is composed of randomly disposed filler filaments providing a predetermined permeability, porosity and void opening which gives the resulting fabric qualities desirable for its use as a filter medium, the rack filaments providing tensile strength.

This is a division of copending application Ser. No. 431,030 filed Feb. 8, 1965 now abandoned.

This invention relates to fabrics formed by sewing and to the method of making such fabrics. More particularly, it relates to fabrics in which filaments in one direction are sewn across filaments in another direction. Still more particularly, the invention relates to fabrics in which a non-woven fibrous filler is stabilized and strengthened with strength members to which the filler is sewn with filaments running transversely thereof, and most particularly to such fabrics for filtration media.

Inits preferred form, the fabric is processed for use as a filtration medium. A primary use is in filtering sewage efiluent to aid in purifying our streams, rivers and lakes by removing settleable solids. For such purposes, it has been found preferable and inexpensive to utilize nonwoven fibers formed into a web where the fibers are randomly disposed to produce the porosity, permeability and void openings as are desirable for the particular filtering processes in which it is to be used. Filters made solely of such webs suffer from the disability of mechanical weakness. Therefore, in accordance with the present invention, such webs are sewn to strength members.

The strength members of the fabrics of this invention are often called rack filaments after the manner in which they are ordinarily assembled into the fabrics. The strength members are usually relatively long filaments positioned in a common plane or sheet by a rack during their assembly into the finished fabric. The non-woven web, called filler, is then disposed upon the rack filaments and is sewn thereto by a sewing machine using other filaments referred to herein as the sewn filaments. For many applications, the filaments are then bonded together, as by applying adhesive resins.

Although various sewing stitches are within the scope of the present invention, it is generally preferable to utilize a stitch in which two threads or sewn filaments are used 'to make a stitch, one sewn filament running along one side of the fabric and the other sewn filament running along the other side of the fabric. The fabric can then be made two sided; that is, the fabric may have different surface qualities on the respective sides. For example, in some applications the fabric is preferably made with sewn filaments on one side made of abrasion resistant material so as to provide an abrasion resistant surface while at the same time having the sewn filament on the other side of the fabric selected to provide, in association with the non-woven filler, a relatively smooth surface. Also at the same time, the strength members or rack filaments are protected by being buried within the sewn filaments.

Sewn fabric has a number of advantages over woven fabrics, not the least of which is its lower cost. The fabric has important mechanical advantages. For example, the fabric is made with the rack filaments substantially straight, making it stronger than fabrics woven with comparable filaments. In the ordinary course of weaving, both the warp and weft yarns are deformed substantially, resulting in the permanent weakening of the yarns and producing a fabric that is not so strong as fabrics made in accordance with the present invention.

As a filter medium, the fabric derives major advantages from the non-woven filler. The filler is preferably formed of fine fibers of such smaller diameter than can be effectively woven. These fibers are randomly disposed to form the filter and provide a relatively high permeability while providing relatively small void openings; that is, the total opening through the filter is large and permits a large volume of filtrate to pass through while the individual openings are small and stop a large fraction of the solids. For use as a filter medium, it is usually desirable that all of the fibers, and the filler in particular, be non-absorbent of water and water resistant. In this connection, it is usually preferable to use one or combinations of the man-made fibers such as those made from viscose, nylon, polyester, acrylic, fluorocarbon and glass materials, but various of the natural fibers, including cotton, are useful in certain applications. The latter may be appropriately treated, where necessary or desirable, to make the fabric non-absorbent of water and at the same time water resistant. The fabric may include mineral or metal fibers.

For many uses, such as for decorator fabrics used in upholstery or drapery material, it is an advantage of the present fabrics merely to be difierent in appearance and feel from woven fabrics. Particularly because of the nonwoven filler, the fabrics have a greater number of controllable variables involved in their construction making it possible to control the hand, finish, texture, absorbency, abrasion resistance and other qualities to a degree not achieved by woven fabrics.

A primary object of this invention is to provide a fabric made by sewing wherein a plurality of substantially straight rack filaments are disposed in a common sheet and a plurality of sewn filaments are stitched in closely spaced rows transversely across the rack filaments.

Another object of the present invention is to provide such a fabric in which the rack filaments provide tensile strength for the fabric in the rack direction and the sewn filaments provide particular qualities for the surfaces of the fabric.

Still another object of the invention is to provide a fabric made by sewing wherein non-woven filler formed of filler filaments is disposed upon the rack filaments and sewn thereto by sewn filaments.

Another object of the invention is to provide a filter medium which passes a large volume of filtrate while stopping a large fraction of settleable solids.

It is still another object of the invention to provide a filter medium in which non-woven filler formed of filler filaments is sewn to the rack filaments with the non-woven filler providing permeability, porosity and void openings required for the filter quality of the medium and with the rack filaments providing strength for the filter medium.

Still another object of the invention is to provide such a filter medium for filtering sewage effluent.

It is still another object of the present invention to provide such a filter for a Fourdrinier machine wherein the inside surface of the filter medium is abrasion resistant and the outside is smooth.

It is still another object of this invention to provide methods for forming such fabrics.

Further objects and advantages of the present invention will become apparent from consideration of the following description taken in conjunction with the accom panying drawings wherein:

FIGURE 1 is a plan view of a piece of sewn fabric made according to the present invention;

FIGURE 2 is a cross-sectional view of the fabric taken along section 22 of FIGURE 1;

FIGURE 3 is a cross-sectional view of the fabric taken along section 33 of FIGURE 1;

FIGURE 4 is an illustration of one form of apparatus for making the fabric of the present invention; and

FIGURE 5 is an illustration of a modified form of apparatus for making the fabric of the present invention in endless form.

In the preferred form of the invention illustrated in FIGURES 1, 2 and 3, the fabric is formed of a plurality of relatively straight and parallel rack filaments 12 lying substantially in a sheet or layer which is disposed a filler 14 which is sewn to the rack filaments 12 by sewn filaments 16 and 18. Only a portion of the fabric is illustrated in FIGURE 1. The fabric ordinarily takes the form of a sheet, that is, it is thin relative to its width and length. However, although the rack filaments are described as being relatively straight or parallel and lying in a sheet or layer and forming a sheet-like fabric, this includes the formation of an endless belt even though the latter requires that the sheet itself be curved and not entirely planar. As shown, the filler 14 is non-woven and is preferably formed of filler filaments 20 of predetermined diameter and length, depending upon the particular application to which the fabric is to be put. In general it is preferable that the filler filaments be long relative to the space between rows of sewn filaments 16, 18 in order that filler filaments bridge the gap between sewn filaments and add their strength to the fabric.

In the fabric illustrated in FIGURE 1, a lock stitch was employed to sew the filler to the rack filaments; however, other stiches can be employedwithin the scope of this invention. In using a lock stitch, it is frequently desirable, as shown, to utilize different threads on the respective sides of the rack filaments. As illustrated in FIG- URE l, the sewn filaments 16 on the filler side of the rack filaments are relatively fine whereas the sewn filaments 18 on the other side of the rack filaments are relatively coarse. Further, the sewn filaments 18 are, as shown, relatively straight, providing certain advantages in some applications. Two-sidedness may be provided by stitches other than the lock stitch. For example, a two filament chain stitch can be used with different sewn filament materials on the respective sides of the fabric. Of course, in many instances it is quite satisfactory to use the same material and filament size on both sides, in which case a single filament chain stitch can be used as well as any of the two filament stitches.

In FIGURE 4 is illustrated one way in which the fabric of FIGURES 1 to 3 can be made. The rack filaments 12 may be supplied by respective reels 22. The rack filaments are passed over a rack 24 which may have a plurality of slots 26 or other means for guiding the relative position of the respective rack filaments 12. The filler 14 may be supplied, as shown, from a supply drum 28 in the form of a sheet. This sheet is directed, as by a roll 30, to place the filler sheet 14 in contact with the rack filaments 12. A sewing machine head 32 is mounted on a bracket 34 which is moved by motive means not shown so as to traverse the rack 24 transversely of the rack filaments 12. The sewing machine head 32 carries sewn filament 18 to the needle 36. At the same time, a bobbin (not shown) is mounted on bracket 34 beneath the rack 24 to supply the sewn filament 16 so that as the sewing machine head 32 traverses the rack filament sewn filaments 16 and 18 lock together around the filler and rack filaments, thus sewing the filler to the rack filaments. Preferably, the traversal of the sewing machine head and its stitching actions are programmed so that the stitches occur between rack filaments 12 rather than at a rack filament, thus avoiding piercing the rack filaments and reducing their strength. Piercing of the rack filaments may also be avoided by using a needle too dull to pierce the filaments. This is particularly effective when the rack filaments ars monofilaments, i.e., single rods.

The rack filaments and filler are advanced after each traversal of the sewing head by a predetermined distance to provide the desired spacing between rows of stitches. The completed fabric is then taken up on a take-up reel 38. Conventional braking means is applied to the respective reels 22 to resist the advance of take-up reel 38 and, therefore, keep the rack filaments 12 under suitable tension so as to keep them substantially straight and parallel in the rack 24 during the sewing operation.

After the filler 14 has been sewn to the rack filament 12, it is frequently desirable and sometimes necessary to treat the fabric further. In many applications, it is desirable to treat the fabric with suitable resin acting to bond the various filaments together. If the fabric is to be used for filtering, care must be taken not to block or blind the passages through the fabric. For some other uses, sufficient resin may be added to block all of the openings including the holes made in sewing. The needle holes may also be reduced or eliminated by shrinking the filler about the needle holes. This may be achieved by applying a controlled amount of heat, which heat may be applied during the curing of the resin.

There are various alternative ways of making the fabric. For example, the rack filaments may be looped around pegs at the end of a rack, and the fabrics sewn as individual sheets rather than in long strips as described in connection with FIGURE 4. Alternatively, it is frequently desirable to make an endless belt as for a Fourdrinier wire. In such instances, the fabric may be made by apparatus as shown in FIGURE 5. In this case, the rack filaments 12 are disposed endlessly about a plurality of rolls 40. At least one of the rolls is adjustable, as by movement of brackets 42, to make the loop of rack filaments 12 the appropriate length and to maintain appropriate tension in the respective filaments. In disposing the rack filaments 12 endlessly, it may be desirable to splice them individually, in which case they are preferably spliced at different positions along the length of the endless belt in order that the belt will not be particularly weakened at the same place for each rack filament. Alternatively, the rack filaments 12 may be formed by a single strand wound helically around the rolls so as to minimize splicing. In the arrangement shown in FIGURE 5, the filler 14 is supplied from the roll 28 to the top of the rack filaments 12. Other than as occasioned by these structural modifications, the apparatus of FIGURE 5 may be operated substantially as described above in connection with FIGURE 4, and the fabric may be finished in a similar manner. A sloping forward surface 44 may be formed in the rack 24 so as the previously sewn part of the endless fabric approaches the sewing head 36, the sewn filaments ride against the surface 44, lifting the rack filaments out of the slots 26 and permitting the fabric to advance until the entire fabric is sewn.

In addition to the advantages of the fabric as made with the apparatus shown in FIGURE 4, the endless belt made in this fashion has an additional advantage over woven belts. It does not shrink in the process of manufacture. That is, the rack filaments are held straight during the process of manufacture and are not deformed by sewing, whereas in the process of weaving, the warp and weft yarns are bent around each other, thus shortening them. In the manufacture of the fabric of the present invention, the rack filaments 12 may be formed into endless loops of precisely the desired length and remain at that same length in the sewing process.

Fabrics made as described above can be used in a number of different applications, many of them requiring quite different properties for the fabric. For each application, there are particular desirable properties for the fabric. These properties may be provided by appropriate selection of the rack filaments, sewn filaments and filler. For example, a a filter medium the permeability, porosity and mean and largest void openings of the fabric should be different for different filtering operations. These properties can be effectively controlled by control of the filament diameter and filament length of the filler filaments 20 and by the thickness of the filler 14.

The strength of the fabric is largely determined by the number, diameter and distribution ofthe rack filaments and by the particular material from which the rack filaments are made. For certain purposes, it is desirable that the fabric have more strength in certain areas, such as at the edge or in the center, in which event the rack filaments can be concentrated in those areas, or filaments of different diameter used. It is also within the scope of this invention to lay strength filaments across the rack filaments and sew them to the rack filaments to strengthen the fabric in the cross direction. It is also within the present invention to place rack filaments in some instances on both sides of the filler and in other instances to have the filler on both sides of the rack filaments.

The abrasion resistance of the fabric may be controlled by control of the sewn filament diameter, the material of which the sewn filaments are made, and by spacing of the sewn filaments and the sewing stroke. At the same time, other surface qualities of the fabric may be achieved. For example, finer sewn filaments may be used to provide a smooth fabric. As stated above, it is possible to have one type of sewn filament on one side of the fabric and another type of sewn filament on the other side of the fabric to provide different qualities for the respective surfaces of the fabric. The number, size and distribution of rack filaments 12 may also affect the relative smoothness of the fabric.

EXAMPLE I With the above criteria in mind, the example of a filter medium can be considered. In particular, a filter medium designed for filtering papermill efifuent will be considered. In such filters, it is desirable to remove as much of the solids as possible while handling a substantial volume of water. For example, in one operating mill it is desirable to filter 50,000 gallons of effluent per minute while removing about 100 tons per day of solid.

In the past, it has been the practice to utilize virgin pulp as the filter medium. Typically, such filters removed about 0.1 pound of solid per square foot per minute while passing about 2 gallons of filtrate per square foot per minute at a pressure differential of about 6 inches of mercury. Typically this left in the filtrate about .25 to 1.4 pounds of solids per 1,000 gallons of filtrate.

A fabric designed pursuant to the present invention has proved to retain 0.15 pound of solids per square foot per minute while passing 6 gallons of filtrate per square foot per minute at the same pressure drop of 6 inches of mercury. At the same time, this filter medium of the present invention passed only about 0.05 to 0.06 pound of solids per 1,000 gallons of filtrate. Thus, the fabric of the present invention in the design tested, removed 50 percent more solids while passing three times as much water and left the filtrate with less than a fourth to a twentieth as much solids.

The filter medium thus tested was made with filler 14 made from very fine filler filaments 20 formed of polyester material as sold under the trademark Dacron. These filaments were prepared in a sheet form known and sold under the trademark Spunbonded. The diameter of the filaments 20 was about 1.5 mils and their average length was about 1.25 inches. The filler was used in sheets about 10 mils thick in which the fibers were bonded by resin. The filler 14 was placed on rack filaments 12 made of Dacron of 660 denier distributed uniformly with 16 filaments per inch. The sewn filaments 16 over the filler were 5.5 mill monofilaments of nylon. The sewn filaments 18 on the other side of the rack filaments were substantially heavier being 440 denier of Dacron. The rows of stitches were uniformly distributed at 12 rows per inch, and the stitches were placed discretely between the rack filaments at 16 per inch. All of the material in this filter fabric was non-absorbent of water.

The improvement in filtering properties lies both in increased permeability and in smaller void openings. This is partly occasioned by the use of fine, long filler filaments. That is, the finer fibers permit a larger total void space (permeability) while making the individual void spaces smaller. The filter therefore permits more water to pass through while stopping smaller particles.

EXAMPLE II Another example of fabric made according to the present invention is a Fourdrinier wire or forming fabric. Such fabrics are formed as endless belts with the rack filaments 12 running in the belt direction to provide the necessary tensile strength to drive the fabric around the papermaking machine. The filler 20 is designed to provide the drainage necessary for the particular papermaking machine and, together with the top sewn filament 16, provides a smooth upper surface on which to form the paper web. At the same time, the sewn filament 18 inside the loop of the fabric 10 is made abrasion resistant to preserve the rack filaments 12 from wear as the fabric passes over the machinery, as for example, over the usual suction boxes. As in the case of the previous example, all of the material is non-absorbent of water.

A typically Fourdrinier fabric is made as follows according to the present invention: The filter material is made of Dacron filaments prepared in the sheet form known and sold under the trademark Spunbonded. The rack filaments are Dacron filaments of 220denier distributed uniformly at 32 filaments per inch. The top sewn yarn is 220 denier Dacron and the inside sewn filament is denier Dacron. The sewn filaments are stitched at rows uniformly distributed with 32 rows per inch and with the stitches discretely between rack yarns at 32 stitches per inch.

Such Foundrinier fabric provides a more rugged fabric than has heretofore been formed by Weaving with filaments of comparable weight. At the same time, the drainage properties are improved by use of the non-woven filler, and the use of fine filler filaments and fine upper sewn filaments provides a smoother surface upon which to form the paper web than has been prevously achieved with Fourdrinier fabrics of comparable drainage rate and strength.

Although various preferred embodiments of the invention have been described above, numerous modifications thereof are within the present invention. As noted above, the types and sizes of filaments vary from application to application. Various sewing stitches may be utilized. The fabric may be formed endlessly or flat. The permeability, porosity and void openings of the filter medium may be varied for particular applications. Indeed for certain applications, the filler may be entirely omitted. Various elements of the fabric can be varied to control the hand, finish, texture, absorbency, abrasion resistance and other qualities to a degree not achieved by woven fabrics.

For most uses, it is the non-woven filler that provides most of the primary qualities of the fabric, with the rack and sewn filaments providing mechanical support and strength. For example, as noted above, in the case of filter media, the permeability and void openings are principally determined by the filler. In the case of Fourdrinier forming fabric, the filler provides most of the smoothness as well as the filtering properties. In the case of a conveyor belt for fragile articles, the filier provides the desired padding and softness. In the case of upholstery fabrics, the filler contributes substantially to the hand, finish and texture, as weli as padding. In the case of drapery material or wall covering, the essential appearance can be derived from the filler. In the case of absrbent fabrics such as wet felts for paper making, the nonwoven filler supplies most of the absorbency.

The materials of which the filaments are made can be varied to suit the particular application. For example, in the case of filter media, the materials must be compatible with the pH end temperature of the material being filtered. As noted in the above examples, the materials are usually preferred to be non-absorbent of water, but in some applications this is not necessary or even desirable.

The invention is limited only by the claims.

What is claimed is:

1. A non-woven filter medium formed by sewing comprising a plurality of substantially straight rack filaments disposed laterally separate substantially in a layer, nonwoven filler formed of randomly disposed filler filamenm providing predetermined permeability, porosity and void opening and disposed adjacent said layer of rack filaments on one side thereof, and a plurality of sewn fila ments stitched in discrete rows over said filler filaments and rack filaments, thereby sewing said rack filaments together and to said filler filaments, said rows being substantially straight and parallel across the entire layer of rack filaments and substantially normally of said rack fiaments, said rack filaments providing tensile strength for said filter medium, and said fiiier providing the filtering quality of said filter medium.

2. A non-woven filter medium formed by sewing comprising a plurality of substantially straight rack filaments disposed laterally separate substantially in a layer, nonwoven filler formed of randomly disposed filler fiaments providing predetermined permeability, porosity and void opening and disposed adjacent said layer of rack filaments on one side thereof, and a plurality of sewn filaments stitched in discrete rows over said filler filaments and rack filaments, thereby sewing said rack filaments together and to said filler filaments, said rows being substantially straight and parallel across the entire layer of rack filaments and substantially normally of said rack filaments, said rack filaments providing tensile strength for said filter medium, said filler providing the filtering quality of said filter medium, and said filler filaments being long relative to the spacing between said rows.

3. A non-woven filter medium formed by sewing comprising a plurality of substantially straight rack filaments disposed laterally separate substantially in a layer, a lurality of randomly disposed filler filaments of predetermined diameter and length formed into a filler of predetermined thickness providing predetermined permeability, porosity and void opening and disposed adjacent said layer of rack filaments on one side thereof, a plurality of sewn filaments stitched in discrete rows over said filler filaments and rack filaments, thereby sewing said filler filaments to said rack filaments and said rack filaments together, said rows being substantially straight and parallel across the entire layer of rack filaments and substantially normally of said rack filaments, said rack filaments providing tensile strength for said filter medium, and said filler providing the filtering quality of said filter medium.

4. A non-woven filter medium formed by sewing comprising a plurality of substantially straight rack filaments disposed laterally separate substantially in a layer, a nonwoven filler formed of randomly disposed filler filaments providing predetermined permeability, porosity and void opening and disposed adjacent said layer of rack filaments on one side thereof, a plurality of first sewn filaments dis posed on the side of said filler opposite said rack filaments, and a plurality of second sewn filaments disposed on the other side of said rack filaments, said first and second sewn filaments being stitched together in discrete rows over said filler filaments and rack filaments, thereby sewing said rack filaments together and to said filler filaments, said rows being substantially straight and parallel across the entire iayer of rack filaments and substantially normally of said rack filaments, said rack filaments providing tensile strength for said filter medium, said filler providing the filtering quality of said filter medium, said first sewn filaments providing a first quality to one surface of said filter medium, and said second sewn filaments providing a second quality to the other surface of said filter medium.

5. A non-woven filter medium for a Fourdrinier machine in the form of a fiat endless belt formed by sewing, said filter medium comprising a plurality of substantially straight and endless rack filaments disposed latera'rly separate substantially in the plane of said belt, nonwoven filier formed of randomly disposed filler filaments providing predetermined permeability, porosity and void opening and disposed adjacent said rack filaments on the outside of said belt, a plurality of first sewn filaments disposed on the outside of said fiiier, and a plurality of second sewn filaments disposed on the inside of said rack filaments, said first and second sewn fiiaments being stitched together in discrete rows over said filter filaments and rac filaments, thereby sewing said rack filaments together and to said filler filaments, said rows being substantially straight and parallel across the entire layer of rack filaments and substantially norma ly of said rack filaments, said rack fiiaments providing tensile strength for said filter medium, said filler providing the filtering quality of said filter medium, said first sewn filaments providing a smooth outer surface for said filter medium, and said second sewn filaments providing an abrasion resistant inner surface for said fiiter medium.

A filter medium according to claim 1 wherein said rack filaments, sewn filaments and filler filaments are nonabsorbent of water.

References Cited UNITED STATES PATENTS 330,236 9/1906 Bell 210-439 X 2,139,675 12/1933 Fleisher 210-434x 2,355,322 3/1944 Rugeley 210 49o 2,416,524 2/1947 Huse et al. 210 439 x 3,153,934 12/1964 Butler.

FOREIGN PATENTS 703,753 5/1965 eanada.

1,053,954 1/1967 Great Britain.

JOHN W. ADEE, Primary Examiner US. Cl. X.R. 

